1. Field of the Invention
The present invention relates to a wireless communication control method and a wireless communication device. More specifically, the invention relates to a wireless communication control method of a wireless communication device employing Adaptive Frequency Hopping (AFH) that switches among a plurality of channels except a channel subject to interference by interference waves in a predetermined frequency band for communication and a wireless communication device thereof.
2. Background Information
A BLUETOOTH communications system employs a Frequency Hopping Spread Spectrum (FH-SS) method providing 79 channels, each with 1 MHz bandwidth, in the 2.4 GHz band (ISM band, i.e., Industrial Scientific Medical Band). The frequency hopping Spread Spectrum method also switches these channels at the rate of 1600 times per second. In the 2.4 GHz band (ISM band), since radio waves from other devices such as wireless Local Area Networks (WLAN) and microwave ovens coexist additionally with radio waves of the BLUETOOTH communications system, the radio waves from other devices may interfere as interfering waves with the radio waves of the BLUETOOTH. In order to reduce mutual interference between the radio waves of the BLUETOOTH and other devices, BLUETOOTH ver 1.2 employs Adaptive Frequency Hopping (AFH) that performs frequency hopping by using channels, which do not interfere with the radio waves from other devices and are restricted to channels that do not suffer from interference.
Japanese Patent Publication JP-A-2001-128232, especially page 2-4, and FIGS. 1-2 thereof, shows a communication channels setting method in the transmission/reception with a plurality of channels, such as Time Division Multiple Access (TDMA), but not to systems like BLUETOOTH with AFH. In the communication channels setting method, signal strength of radio signals is measured by putting a radio frequency (RF) portion in a receiving mode even in the time frames allocated to transmitting channels, and then channels for use are selected depending on the signal strength. Due to this structure, the channels that wireless devices of the same kind use on the perimeter are not selected, and the channels that do not interfere with communications among other wireless devices are selected. Thus, the mutual interference is reduced. Japanese Patent Publication JP-A-2001-128232 is hereby incorporated by reference.
As described above, the BLUETOOTH wireless communication system employs the Adaptive Frequency Hopping (AFH) and this causes mutual interference by interference waves to be reduced. In general, an assessment of the receiving state of each channel is performed by receiving error information, such as information on whether or not sync word error, packet header error, or payload error (e.g., the Cycle Redundancy Check (CRC) error and the Forward Error Connection (FEC) error) exists, and Received Signal Strength Indicator (RSSI) information. The algorithm of the channel assessment method is dependent on algorithm implementation by wireless device makers.
It is conceivable that mutual interference with interference waves from other devices and reduction of signal strength of receiving signals resulting from the degree of physical distance between BLUETOOTH communication devices, for instance, are factors of inducing a receiving error. Further, interference waves from other devices include temporary interference waves and constant or intermittent interference waves, such as interference waves from a WLAN or a microwave oven. The AFH restricts the use of channels in which a receiving error occurred. However, it is not desirable to set an error, such as an error that resulted from temporary interference waves and the mere degree of physical distance, as a target to restrict use of channels in which these errors occurred. This is because the number of channels available for communication decreases by setting these errors as targets to restrict use of channels, and this causes a spreading ratio of transmitting signals to be decreased. Therefore, an algorithm for channel assessment to restrict only use of channels that face mutual interference by constant or intermittent interference waves is required.
The communication channel setting method described in the Japanese Patent Publication JP-A-2001-128232 relates to the WLAN with the TDMA, but not to the system such as BLUETOOTH communication system with AFH.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved wireless communication method and wireless communication device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.